The present invention relates to transfer cases for four-wheel drive vehicles in general, and in particular, to a lubrication system for a chain of a transfer case provided with a dry sump chain reservoir.
Transfer cases for four-wheel drive vehicles are well known in the prior art, and serve to transmit torque from an engine or prime mover to a plurality of drive axles to thereby drive front and rear axles of a motor vehicle. Typically, the transfer case includes an input shaft driven by a vehicle transmission, two output shafts driving front and rear axles and an endless chain element transmitting input torque to the output shaft driving front wheels in a four-wheel drive mode. The transfer case is usually mounted behind and is driven by a transmission. Two shafts normally run from the transfer case: one to the front drive axle and one to the rear drive axle.
Usually, the torque transmitting chain is housed in a common compartment defined by a transfer case casing. The casing is typically provided with an oil bath where the chain is partially immersed. The chain, rotating all the time the vehicle transmission is driven, constantly aerates and churns the lubrication oil that substantially raises the oil temperature, especially at high speeds, thus, significantly deteriorating the quality of oil and reducing the service life of the oil and the transfer case.
The present invention alleviates the drawbacks of the prior art. The present invention provides a transfer case for a four-wheel drive vehicle including a casing having a partition wall defining two separate fluidly isolated compartments: a lubricant reservoir and a torque transfer compartment. The torque transfer compartment houses a chain transmitting power from a driving sprocket to a driven sprocket, and the lubricant reservoir contains an appropriate predetermined amount of the lubricant. While the lubricant reservoir is provided with an oil bath, the torque-transfer compartment is virtually dry and fluidly isolated from the lubricant in the lubricant reservoir by the partition wall and a seal member. In order to provide the needed lubrication, a lubricant dispenser is employed that provides a necessary amount of oil in a chain sprocket area. The motion of the chain throws the excess oil out of the torque-transfer compartment back onto the lubricant reservoir so that only a small amount of oil would be in the torque-transfer compartment. Therefore, the aeration and churning of the oil is prevented and the temperature of the lubrication oil is reduced.